1. Field of the Invention
The present invention relates to an apparatus and a method of coating flux. It particularly relates to an apparatus and a method of coating flux on a printed circuit board pinpointing at only necessary point(s) for local soldering.
2. Description of Related Art
The printed circuit board has formerly been soldered by a flow soldering in an automatic soldering apparatus having a soldering bath in which rod-like solder or line-like solder is melted on several reasons such that equipment for the flow soldering is inexpensive costly even if peripheral equipment is included, the flow soldering has high reliability as the soldering and parts for the flow soldering is easily available because parts with a lead wire is easily manufactured.
In recent years, the soldering method has shifted from the flow soldering to a reflow soldering that is suitable for the soldering of small surface mount device as a demand to use any small electronic equipment rises according to popularity of portable equipment. In the reflow soldering, the surface mount device passes through a reflow oven having heated temperature of 220° C. through 250° C. for a period of time of one minute or more so that any higher heat-resisting property is necessary for the surface mount device for the reflow soldering compared with that of any past device for the flow soldering. Further, as solder used for the soldering, past Sn—Pb solder with a melting temperature of 183° C. has been recently replaced with lead-free solder, for example, Sn—3.0mass%Ag—0.5mass%Cu, having a melting temperature of 220° C., which also may require an electronic parts having any higher heat-resisting property, in order to counter an environmental issue.
Thus, the shift of the soldering method from the flow soldering to the reflow soldering or the replacement of the past Sn—Pb solder with the lead-free solder has been facilitated. There are, however, many electronic parts having no structure-based heat-resisting property that may be necessary for these soldering methods. For example, precision semiconductor such as a micro processor unit (MPU), a connection part such as a connecter and a switch in which the exterior thereof is plastic, or aluminum electrolytic condenser containing electrolyte therein is illustrated. Many parts thereof presently may have been retrofitted by using a soldering iron, a partial flow soldering apparatus or the like.
In the soldering of the partial flow soldering apparatus, when the flux is coated on a whole of a surface to be soldered of the printed circuit board, it is necessary to clean the flux coated on any unnecessary portions, which causes a manufacture cost to be increased. When the flux is inserted into a loading slot of a jack of a connecter mounted on the surface to be soldered of the printed circuit board, it may become impossible as the connecter. This results in a case where the flux is coated on only any necessary portions. Therefore, the flux is coated manually or by using the partial flow soldering apparatus that can coat the flux on only any necessary portions. Such a manual flux coating reduces operating efficiency because a human do so. Further, its results are dependent on some experience of a person who executes the manual flux coating so that skilled labor may be required. Such skilled labor is not easy to be trained.
An apparatus of coating the flux, which has been formerly used to coat the flux efficiently on only the necessary portions, is a foaming typed apparatus of coating the flux. Namely, the flux is foamed from a surface of porous hollow material contained in the nozzle by supplying air into the porous hollow material and the nozzle supplies the foamed flux that has been inflated by the foaming upward to coat it on a part to be partially soldered of the printed circuit board and a lead wire. Such a foaming typed apparatus of coating the flux, however, may require any maintenance such that the flux is foamed in a solvent in order to prevent the porous hollow material from being clogged by the foamed flux. Further, a diluent is used in order to control a specific gravity of the solvent, thereby increasing the manufacturing cost.
The apparatus of coating the flux contains a spray typed apparatus of coating the flux other than the foaming typed apparatus of coating the flux. Japanese Patent Application Publication NO. H02-112876 has disclosed an invention in which the flux is coated on a printed circuit board through an opening of a palette using the spray typed apparatus of coating the flux.
Japanese Patent Application Publication NO. H11-177226 has disclosed an invention in which a mask nozzle having an opening which is almost the same shape as that of a group of parts to be soldered of a printed circuit board is used in order to coat the flux on only the group of parts to be soldered of the printed circuit board as a method of coating the flux partially on the printed circuit board.
Japanese Patent Application Publication NOS. H10-22618, 2003-124621 and 2003-179336 have respectively disclosed inventions relating to spray typed apparatuses and methods of coating the flux in each of which an outlet is provided near a nozzle in order to discharge excessive flux.
Japanese Patent Application Publication NO. 2002-290024 has disclosed an invention relating to a method of dipping a part to be soldered of a printed circuit board directly into flux. Specifically, the part to be soldered of the printed circuit board is dipped into liquid that is made by diluting a flux solution with volatile solvent.
Japanese Patent Application Publication No. 2008-177437 has disclosed an invention relating to a method of coating flux in which a lead pin is provided with recesses that hold a necessary amount of flux. In this invention, an amount of flux that is necessary for soldering is previously calculated. The lead pin is provided with recesses that have volume of holding a calculated amount of flux. Next, the lead pin with the recesses is dipped into the flux to hold the flux on the recesses.
Japanese Patent Application Publication NO. 2002-368401 has disclosed an invention relating to a method of coating flux utilizing capillary phenomenon. In this invention, a container filled with flux is provided with penetration members and by utilizing the capillary phenomenon, the flux is penetrated to the penetration members. The flux is coated on the printed circuit board by contacting the penetration members with a part to be soldered of the printed circuit board.
Japanese Patent Application Publication NO. 2000-13007 has disclosed an invention relating to a method of coating flux by utilizing the capillary phenomenon under the pressure of gas. In this invention, a container containing the flux is provided with small holes at positions corresponding to parts of a printed circuit board, on which the flux is to be coated, and then this container is inclined or the flux is flown into or out of the container so that the flux is adhered to an interior of each of the small holes. The flux is coated on the printed circuit board by flowing gas into the container from a gas inlet pipe connecting the container. Alternatively, flux-solution-sending pipes connect the small holes and forward ends of the flux-solution-sending pipes connect the printed circuit board or come close to the printed circuit board. Next, by supplying gas from the gas inlet pipe, the flux is coated on the printed circuit board.